[RFA/mips] 128-bit long doubles for N32/N64

[Andrew Cagney]

>>Does long_double's floatformat need to be set?
> 
> 
> Apparently not. Or I should say that I don't see any evidence that
> it should.

Check the floating-point tests in structs.exp and call-sc.exp.  There's 
hopefully also some sort of floating-point.exp test that confirms the 
basics.

Looking at the code, it appears to default to:

const struct floatformat *
default_double_format (struct gdbarch *gdbarch)
{
   int byte_order = gdbarch_byte_order (gdbarch);
   switch (byte_order)
     {
     case BFD_ENDIAN_BIG:
       return &floatformat_ieee_double_big;
     case BFD_ENDIAN_LITTLE:
       return &floatformat_ieee_double_little;
     default:
       internal_error (__FILE__, __LINE__,
                       "default_double_format: bad byte order");
     }
}

outch!

Andrew